package main

// Betterbird as the tools see it. Betterbird is the mail client's one process tree: the main process
// (comm betterbird-bin, no -contentproc) owns every window — the mail window, the calendar's reminder
// dialog, the composer — and its children (-contentproc) render add-ons and media. The tools read only:
//   - the account's processes, and of the main process where its output goes (fd 1 and 2) and which
//     profile it holds open;
//   - profiles.ini, to find the profile, and the profile's prefs.js and user.js, of which only the
//     preferences asked for are answered and never one that can hold a credential or names an account
//     (passwordSecret, accountPrefix);
//   - the profile's extensions.json, for the add-ons' ids and whether each is on;
//   - the module's declared user.js (~/.config/betterbird/user.js), which the node-engine writes from
//     the module's setting `prefs`.
//
// Never read: the mail store, the address books, logins.json, key4.db, cert9.db, cookies, the
// calendar's caches. Nothing of the operator's mail, calendar or accounts is answered.
//
// The one file a tool writes in the profile is user.js, and only the module's own: the declared file,
// copied whole (betterbird_user_js with apply, betterbird_restart). A user.js that is not the module's
// is never overwritten.

import (
	"bufio"
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"time"
)

const (
	mainComm   = "betterbird-bin"
	startBin   = "/usr/bin/betterbird"
	packageFor = "betterbird-bin"
	appIni     = "/opt/betterbird/application.ini"
	restartAs  = "mesh-betterbird"
	testUnit   = "mesh-betterbird-reminder-test"
	// profilesDir is where Betterbird keeps its profiles: Thunderbird's place, which Betterbird shares.
	profilesDir = ".thunderbird"
	// declared is the module's user.js, written by the node-engine from the setting prefs.
	declared = ".config/betterbird/user.js"
	// mark is the first line of the module's user.js: how a user.js is known to be the module's.
	mark = "// Betterbird's user.js (module betterbird"
)

// readLink is how a process's file descriptors are read; tests replace it, so no test makes a link.
var readLink = os.Readlink

// mainProcs are Betterbird's main processes: comm betterbird-bin without -contentproc.
func (m *Machine) mainProcs() []Proc {
	var out []Proc
	for _, p := range m.procs(mainComm) {
		// The reminder test's Betterbird is never the operator's: its command line names its own profile.
		if !strings.Contains(p.Command, "-contentproc") && !strings.Contains(p.Command, testUnit) {
			out = append(out, p)
		}
	}
	return out
}

// Stream is where a process's standard output or error goes.
type Stream struct {
	FD   int    `json:"fd"`
	Goes string `json:"goes"`
	// Dead is a pipe no process of the account reads: a write there fails.
	Dead bool `json:"dead,omitempty"`
}

// streams says where fd 1 and 2 of a process go.
func (m *Machine) streams(pid int) []Stream {
	var out []Stream
	for _, fd := range []int{1, 2} {
		target, err := readLink(m.path(fmt.Sprintf("/proc/%d/fd/%d", pid, fd)))
		s := Stream{FD: fd}
		switch {
		case err != nil:
			s.Goes = "unreadable"
		case target == "/dev/null":
			s.Goes = "discarded (/dev/null)"
		case strings.HasPrefix(target, "socket:"):
			s.Goes = "a socket (the journal, when started by the module)"
		case strings.HasPrefix(target, "pipe:"):
			if r := m.pipeReaders(target, pid); len(r) > 0 {
				s.Goes = "a pipe read by " + strings.Join(r, ", ")
			} else {
				s.Goes, s.Dead = "a pipe nobody reads", true
			}
		default:
			s.Goes = m.tilde(target)
		}
		out = append(out, s)
	}
	return out
}

// pipeReaders are the account's processes holding the pipe open for reading (O_RDONLY in fdinfo).
func (m *Machine) pipeReaders(pipe string, except int) []string {
	entries, _ := os.ReadDir(m.path("/proc"))
	seen := map[string]bool{}
	var out []string
	for _, e := range entries {
		pid, err := strconv.Atoi(e.Name())
		if err != nil || pid == except {
			continue
		}
		dir := m.path(filepath.Join("/proc", e.Name()))
		if m.uidOf(dir) != m.UID {
			continue
		}
		fds, _ := os.ReadDir(filepath.Join(dir, "fd"))
		for _, fd := range fds {
			if t, err := readLink(filepath.Join(dir, "fd", fd.Name())); err != nil || t != pipe {
				continue
			}
			if readOnly(readTrimmed(filepath.Join(dir, "fdinfo", fd.Name()))) {
				name := fmt.Sprintf("%s (pid %d)", readTrimmed(filepath.Join(dir, "comm")), pid)
				if !seen[name] {
					seen[name] = true
					out = append(out, name)
				}
			}
		}
	}
	sort.Strings(out)
	return out
}

// readOnly reads an fdinfo's flags (octal): the access mode is its low two bits, 0 for reading.
func readOnly(fdinfo string) bool {
	for _, l := range strings.Split(fdinfo, "\n") {
		if f := strings.Fields(l); len(f) == 2 && f[0] == "flags:" {
			n, err := strconv.ParseInt(f[1], 8, 64)
			return err == nil && n&3 == 0
		}
	}
	return false
}

// iniSections reads an INI file into its sections, in order.
func iniSections(raw []byte) (names []string, sections map[string]map[string]string) {
	sections = map[string]map[string]string{}
	cur := ""
	s := bufio.NewScanner(bytes.NewReader(raw))
	for s.Scan() {
		l := strings.TrimSpace(s.Text())
		switch {
		case l == "" || strings.HasPrefix(l, ";") || strings.HasPrefix(l, "#"):
		case strings.HasPrefix(l, "[") && strings.HasSuffix(l, "]"):
			cur = l[1 : len(l)-1]
			if _, ok := sections[cur]; !ok {
				names = append(names, cur)
				sections[cur] = map[string]string{}
			}
		default:
			if i := strings.IndexByte(l, '='); i > 0 && cur != "" {
				sections[cur][strings.TrimSpace(l[:i])] = strings.TrimSpace(l[i+1:])
			}
		}
	}
	return names, sections
}

// Profile is the profile the tools act on, and how it was found.
type Profile struct {
	Dir     string `json:"dir"`
	FoundBy string `json:"found_by"`
	path    string
}

// profile finds the profile: the one the running Betterbird holds open, else the installation's
// default in profiles.ini ([Install…] Default), else the profile marked Default=1.
func (m *Machine) profile() (Profile, error) {
	base := m.home(profilesDir)
	if ps := m.mainProcs(); len(ps) > 0 {
		counts := map[string]int{}
		fds, _ := os.ReadDir(m.path(fmt.Sprintf("/proc/%d/fd", ps[0].PID)))
		for _, fd := range fds {
			t, err := readLink(m.path(fmt.Sprintf("/proc/%d/fd/%s", ps[0].PID, fd.Name())))
			if err != nil {
				continue
			}
			rel, err := filepath.Rel(filepath.Join(m.Home, profilesDir), t)
			if err != nil || strings.HasPrefix(rel, "..") || !strings.Contains(rel, "/") {
				continue
			}
			counts[strings.SplitN(rel, "/", 2)[0]]++
		}
		best, n := "", 0
		for d, c := range counts {
			if c > n || (c == n && d < best) {
				best, n = d, c
			}
		}
		if best != "" {
			return Profile{Dir: m.tilde(filepath.Join(m.Home, profilesDir, best)), path: filepath.Join(base, best),
				FoundBy: fmt.Sprintf("held open by the running Betterbird (pid %d, %d files)", ps[0].PID, n)}, nil
		}
	}
	raw, err := readBounded(filepath.Join(base, "profiles.ini"))
	if err != nil {
		return Profile{}, fmt.Errorf("no profile: Betterbird is not running and ~/%s/profiles.ini is unreadable (%v)", profilesDir, err)
	}
	names, sections := iniSections(raw)
	pick := func(rel string, by string) (Profile, error) {
		dir := filepath.Join(base, filepath.FromSlash(rel))
		if filepath.IsAbs(rel) {
			dir = m.path(rel)
		}
		if !strings.HasPrefix(filepath.Clean(dir), filepath.Clean(base)+string(filepath.Separator)) {
			return Profile{}, fmt.Errorf("profiles.ini names a profile outside ~/%s: %s", profilesDir, rel)
		}
		return Profile{Dir: m.tilde(strings.TrimPrefix(dir, m.Root)), path: dir, FoundBy: by}, nil
	}
	var installs []string
	for _, n := range names {
		if strings.HasPrefix(n, "Install") && sections[n]["Default"] != "" {
			installs = append(installs, n)
		}
	}
	if len(installs) == 1 {
		return pick(sections[installs[0]]["Default"], "profiles.ini: the installation's default ["+installs[0]+"]")
	}
	for _, n := range names {
		if strings.HasPrefix(n, "Profile") && sections[n]["Default"] == "1" && sections[n]["Path"] != "" {
			return pick(sections[n]["Path"], "profiles.ini: the profile marked Default=1 ["+n+"]")
		}
	}
	return Profile{}, fmt.Errorf("profiles.ini names %d installation defaults and no profile marked default: start Betterbird once, then ask again", len(installs))
}

// prefLine is one user_pref(…) or pref(…) line of prefs.js or user.js.
var prefLine = regexp.MustCompile(`^\s*(?:user_)?pref\(\s*"((?:[^"\\]|\\.)*)"\s*,\s*(.*?)\s*\)\s*;\s*$`)

// readPrefs reads the preferences of a prefs.js or user.js: name to its value, as written.
func readPrefs(raw []byte) map[string]string {
	out := map[string]string{}
	s := bufio.NewScanner(bytes.NewReader(raw))
	s.Buffer(make([]byte, 64<<10), 4<<20)
	for s.Scan() {
		if mm := prefLine.FindStringSubmatch(s.Text()); mm != nil {
			out[mm[1]] = mm[2]
		}
	}
	return out
}

// passwordSecret and accountPrefix say which preferences are never answered with their value: one
// whose name can hold a credential, and one that names an account, a server or a person.
var (
	passwordSecret = regexp.MustCompile(`(?i)(password|passwd|secret|token|oauth|auth|cookie|credential|signon|apikey|api_key|privatekey|private_key|\.key$)`)
	accountPrefix  = []string{"mail.server.", "mail.identity.", "mail.smtpserver.", "mail.smtp.", "mail.account.",
		"mail.accountmanager.", "ldap_2.", "extensions.owl.", "calendar.registry.", "mail.root.", "mailnews.",
		"services.sync.", "mail.displayname", "mail.default_", "mail.last_msg", "messenger.account.", "mail.cloud_files."}
	// allowedExtensions are the only extensions.* preferences answered: the add-ons' own preferences can
	// hold anything, and a theme's id is what a window's look depends on.
	allowedExtensions = map[string]bool{"extensions.activeThemeID": true}
)

// withheld says why a preference's value is never answered, or "" when it may be.
func withheld(name string) string {
	if strings.HasPrefix(name, "extensions.") && !allowedExtensions[name] {
		return "an add-on's own preference: only the theme's id (extensions.activeThemeID) is answered"
	}
	if passwordSecret.MatchString(name) {
		return "its name says it can hold a credential"
	}
	for _, p := range accountPrefix {
		if strings.HasPrefix(name, p) {
			return "it names an account, a server, a calendar or a person"
		}
	}
	return ""
}

// Pref is one preference as the profile holds it.
type Pref struct {
	Name string `json:"name"`
	// Value is what Betterbird uses: user.js's at the start, else prefs.js's. Absent: the default.
	Value    string `json:"value,omitempty"`
	From     string `json:"from,omitempty"`
	Withheld string `json:"withheld,omitempty"`
}

// mostPrefs bounds how many preferences one answer carries.
const mostPrefs = 200

// Prefs answers the named preferences (a name, or a prefix ending in . or *) from the profile.
func (m *Machine) Prefs(names []string) (map[string]any, error) {
	if len(names) == 0 {
		return nil, errors.New("names is required: preferences by name, or a prefix ending in . or *, e.g. calendar.alarms.")
	}
	for _, n := range names {
		if strings.Trim(strings.TrimSpace(n), ".*") == "" {
			return nil, fmt.Errorf("%q asks for every preference: name one, or a prefix such as calendar.alarms.", n)
		}
	}
	p, err := m.profile()
	if err != nil {
		return nil, err
	}
	prefsJS, _ := readBounded(filepath.Join(p.path, "prefs.js"))
	userJS, _ := readBounded(filepath.Join(p.path, "user.js"))
	fromPrefs, fromUser := readPrefs(prefsJS), readPrefs(userJS)
	all := map[string]bool{}
	for n := range fromPrefs {
		all[n] = true
	}
	for n := range fromUser {
		all[n] = true
	}
	var out []Pref
	cut := false
	seen := map[string]bool{}
	for _, want := range names {
		prefix := strings.HasSuffix(want, ".") || strings.HasSuffix(want, "*")
		want = strings.TrimSuffix(want, "*")
		var matched []string
		if prefix {
			for n := range all {
				if strings.HasPrefix(n, want) {
					matched = append(matched, n)
				}
			}
			sort.Strings(matched)
		} else {
			matched = []string{want}
		}
		for _, n := range matched {
			if seen[n] {
				continue
			}
			seen[n] = true
			if len(out) == mostPrefs {
				cut = true
				break
			}
			pr := Pref{Name: n}
			v, from := fromPrefs[n], "prefs.js"
			if u, ok := fromUser[n]; ok {
				v, from = u, "user.js (wins at the start)"
			} else if _, ok := fromPrefs[n]; !ok {
				from = "not set: Betterbird's default"
				v = ""
			}
			pr.From = from
			if why := withheld(n); why != "" {
				pr.Withheld = why
			} else if allowedExtensions[n] {
				pr.Value = v
			} else {
				pr.Value = m.maskValue(v)
			}
			out = append(out, pr)
		}
	}
	answer := map[string]any{"profile": p, "prefs": out}
	if cut {
		answer["cut"] = fmt.Sprintf("the first %d; ask for a narrower prefix", mostPrefs)
	}
	return answer, nil
}

// statement is the one thing a line of the module's user.js may be, beside a comment.
var statement = regexp.MustCompile(`^user_pref\("[A-Za-z0-9_.\-\[\]]+",\s*(true|false|-?[0-9]+|"(?:[^"\\]|\\.)*")\);$`)

// validUserJS says what is wrong with a user.js the module would place, or nil. It holds comments and
// user_pref(…) statements only — the setting is one line, so several statements may share one — and
// sets no preference whose name could hold a credential.
func validUserJS(text string) error {
	if !strings.HasPrefix(text, mark) {
		return fmt.Errorf("it does not begin with the module's mark (%q)", mark)
	}
	for i, line := range strings.Split(text, "\n") {
		line = strings.TrimSpace(line)
		if line == "" || strings.HasPrefix(line, "//") {
			continue
		}
		for _, st := range splitStatements(line) {
			if st == "" || strings.HasPrefix(st, "//") {
				continue
			}
			if !statement.MatchString(st) {
				return fmt.Errorf("line %d holds %q, which is not user_pref(\"name\", value);", i+1, st)
			}
			name := st[len(`user_pref("`):strings.Index(st, `",`)]
			if passwordSecret.MatchString(name) {
				return fmt.Errorf("line %d sets %s, a preference that can hold a credential: not through the mesh", i+1, name)
			}
		}
	}
	return nil
}

// splitStatements cuts a line after each `);`, outside a string.
func splitStatements(line string) []string {
	var out []string
	in, esc, start := false, false, 0
	for i := 0; i < len(line); i++ {
		c := line[i]
		switch {
		case esc:
			esc = false
		case c == '\\' && in:
			esc = true
		case c == '"':
			in = !in
		case c == ';' && !in:
			out = append(out, strings.TrimSpace(line[start:i+1]))
			start = i + 1
		}
	}
	if rest := strings.TrimSpace(line[start:]); rest != "" {
		out = append(out, rest)
	}
	return out
}

// UserJS is the module's user.js against the profile's.
type UserJS struct {
	Declared   string `json:"declared"`
	Present    bool   `json:"declared_present"`
	Valid      string `json:"declared_problem,omitempty"`
	Profile    string `json:"profile_user_js"`
	Placed     string `json:"placed"`
	Statements int    `json:"statements"`
	// Effective says whether the running Betterbird started after the file was placed.
	Effective string `json:"effective,omitempty"`
	Content   string `json:"content,omitempty"`
	Applied   bool   `json:"applied,omitempty"`
}

// userJS compares the declared user.js with the profile's; apply places the declared one when the
// profile has none or the module's.
func (m *Machine) userJS(apply bool) (UserJS, error) {
	a := UserJS{Declared: "~/" + declared}
	want, err := readBounded(m.home(declared))
	a.Present = err == nil
	p, perr := m.profile()
	if perr != nil {
		return a, perr
	}
	target := filepath.Join(p.path, "user.js")
	a.Profile = m.tilde(strings.TrimPrefix(target, m.Root))
	if a.Present {
		if verr := validUserJS(string(want)); verr != nil {
			a.Valid = verr.Error()
		}
		a.Content = string(want)
		for _, line := range strings.Split(string(want), "\n") {
			for _, st := range splitStatements(strings.TrimSpace(line)) {
				if statement.MatchString(st) {
					a.Statements++
				}
			}
		}
	}
	have, herr := readBounded(target)
	switch {
	case herr != nil:
		a.Placed = "none: the profile has no user.js"
	case a.Present && bytes.Equal(have, want):
		a.Placed = "the module's, as declared"
	case bytes.HasPrefix(have, []byte(mark)):
		a.Placed = "the module's, from an earlier declaration"
	default:
		a.Placed = "not the module's: a user.js of the operator's, which the module never overwrites"
	}
	if apply {
		switch {
		case !a.Present:
			return a, fmt.Errorf("the module's user.js is not on this machine (~/%s): the module is not pushed here yet", declared)
		case a.Valid != "":
			return a, fmt.Errorf("the module's user.js is refused: %s; change the setting prefs", a.Valid)
		case herr == nil && !bytes.HasPrefix(have, []byte(mark)):
			return a, fmt.Errorf("%s is not the module's: move it aside (its preferences belong in the setting prefs), then apply again", a.Profile)
		}
		if herr != nil || !bytes.Equal(have, want) {
			tmp := target + ".mesh-new"
			if err := os.WriteFile(tmp, want, 0o644); err != nil {
				return a, err
			}
			if err := os.Rename(tmp, target); err != nil {
				os.Remove(tmp)
				return a, err
			}
		}
		a.Applied, a.Placed = true, "the module's, as declared"
	}
	if ps := m.mainProcs(); len(ps) > 0 {
		if st, err := os.Stat(target); err == nil {
			if t, err := time.Parse(time.RFC3339, ps[0].Since); err == nil && st.ModTime().After(t) {
				a.Effective = "not yet: Betterbird reads user.js when it starts, and it started before the file was placed (betterbird_restart)"
			} else if err == nil {
				a.Effective = "yes: the running Betterbird started after the file was placed"
			}
		}
	}
	return a, nil
}

// Status is what betterbird_status answers.
type Status struct {
	Running   []Proc   `json:"running"`
	Children  int      `json:"children"`
	Installed string   `json:"installed,omitempty"`
	Foreign   bool     `json:"from_the_aur,omitempty"`
	Version   string   `json:"version,omitempty"`
	Build     string   `json:"build,omitempty"`
	Profile   *Profile `json:"profile,omitempty"`
	Problem   string   `json:"profile_problem,omitempty"`
	Output    []Stream `json:"output,omitempty"`
	UserJS    *UserJS  `json:"user_js,omitempty"`
	AddOns    []AddOn  `json:"add_ons,omitempty"`
	// Display are the preferences that decide how its windows and notifications look.
	Display []Pref `json:"display_prefs,omitempty"`
}

// AddOn is one add-on the operator installed: its id, and whether it is on.
type AddOn struct {
	ID     string `json:"id"`
	Active bool   `json:"active"`
}

// displayPrefs are the preferences betterbird_status answers: the reminder dialog, the theme, the
// renderer, and whether notifications go to the desktop's notifier.
var displayPrefs = []string{"calendar.alarms.playsound", "calendar.alarms.show", "calendar.alarms.showmissed",
	"calendar.alarms.indicator.show", "alerts.useSystemBackend", "mail.biff.use_system_alert",
	"extensions.activeThemeID", "browser.display.use_system_colors", "ui.systemUsesDarkTheme",
	"gfx.webrender.software", "gfx.webrender.all", "layers.acceleration.disabled", "widget.gtk.overlay-scrollbars.enabled",
	"mozilla.widget.use-argb-visuals"}

func (m *Machine) foreign(pkg string) bool {
	o := m.cmd(0, nil, "pacman", "-Qmq", pkg)
	return o.Err == nil && o.Code == 0 && strings.TrimSpace(o.Stdout) == pkg
}

// Status answers whether Betterbird runs, what is installed, its profile and the module's user.js.
func (m *Machine) Status() (Status, error) {
	s := Status{Running: m.mainProcs()}
	if s.Running == nil {
		s.Running = []Proc{}
	}
	s.Children = len(m.procs(mainComm)) - len(s.Running)
	if v, err := m.installed(packageFor); err == nil && v != "" {
		s.Installed, s.Foreign = v, m.foreign(packageFor)
	}
	if raw, err := readBounded(m.path(appIni)); err == nil {
		_, sec := iniSections(raw)
		s.Version, s.Build = sec["App"]["Version"], sec["App"]["BuildID"]
	}
	if len(s.Running) > 0 {
		s.Output = m.streams(s.Running[0].PID)
	}
	p, err := m.profile()
	if err != nil {
		s.Problem = err.Error()
		return s, nil
	}
	s.Profile = &p
	if u, err := m.userJS(false); err == nil {
		u.Content = ""
		s.UserJS = &u
	}
	if raw, err := readBounded(filepath.Join(p.path, "extensions.json")); err == nil {
		var ext struct {
			Addons []struct {
				ID       string `json:"id"`
				Active   bool   `json:"active"`
				Location string `json:"location"`
			} `json:"addons"`
		}
		if json.Unmarshal(raw, &ext) == nil {
			for _, a := range ext.Addons {
				if a.Location == "app-profile" {
					s.AddOns = append(s.AddOns, AddOn{a.ID, a.Active})
				}
			}
		}
	}
	if got, err := m.Prefs(displayPrefs); err == nil {
		s.Display = got["prefs"].([]Pref)
	}
	return s, nil
}

// emailAddress and credentialWord are masked in what Betterbird printed.
var (
	emailAddress   = regexp.MustCompile(`[A-Za-z0-9._%+\-]+@[A-Za-z0-9.\-]+\.[A-Za-z]{2,}`)
	credentialWord = regexp.MustCompile(`(?i)((?:password|passwd|token|secret|authorization|cookie)\S*\s*[=:]\s*)\S+`)
)

// userAtHost and hostName are what a preference's value may name a server by.
var (
	userAtHost = regexp.MustCompile(`[A-Za-z0-9._%+\-]+%40[A-Za-z0-9.\-]+@[A-Za-z0-9.\-]+`)
	// A host is a name of three labels or more, or of two whose last is a common top-level domain: a
	// file's name (a.pdf) is not one.
	hostName      = regexp.MustCompile(`(?i)\b(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.){2,}[a-z]{2,}|[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.(?:com|org|net|be|nl|de|fr|eu|io|uk|us|info|biz|dev|app|cloud|local|lan|internal|home|corp))\b`)
	bearerOrBasic = regexp.MustCompile(`(?i)\b(bearer|basic)\s+[A-Za-z0-9._~+/=\-]+`)
)

func mask(s string) string {
	s = userAtHost.ReplaceAllString(s, "<hidden>")
	s = emailAddress.ReplaceAllString(s, "<hidden>")
	s = bearerOrBasic.ReplaceAllString(s, "$1 <hidden>")
	return credentialWord.ReplaceAllString(s, "${1}<hidden>")
}

// maskValue is a preference's value as answered: the home as ~, and no address, user or host.
func (m *Machine) maskValue(v string) string {
	if m.Home != "" && m.Home != "/" {
		v = strings.ReplaceAll(v, strings.TrimSuffix(m.Home, "/")+"/", "~/")
	}
	v = mask(v)
	return hostName.ReplaceAllString(v, "<host>")
}

// mostAnswer bounds a log answer.
const mostAnswer = 128 << 10

// Log answers the last n lines Betterbird printed, from the journal of the unit the module starts it
// as; problems keeps the lines that say error, warning, crash or assertion. Addresses and credentials
// are masked.
func (m *Machine) Log(n int, problems bool, unit string) (map[string]any, error) {
	if unit == "" {
		unit = restartAs
	}
	if unit != restartAs && unit != testUnit {
		return nil, fmt.Errorf("unit is %s or %s", restartAs, testUnit)
	}
	o := m.cmd(0, m.bus(), "journalctl", "--user", "--unit", unit+".service", "--no-pager", "--output", "short-iso", "-n", strconv.Itoa(n))
	if err := failed(o, "journalctl"); err != nil {
		return nil, err
	}
	var lines []string
	size := 0
	keep := regexp.MustCompile(`(?i)(error|warn|crash|assert|fail|exception)`)
	for _, l := range strings.Split(strings.TrimRight(o.Stdout, "\n"), "\n") {
		if l == "" || (problems && !keep.MatchString(l)) {
			continue
		}
		l = mask(l)
		if size+len(l) > mostAnswer {
			break
		}
		size += len(l) + 1
		lines = append(lines, l)
	}
	if lines == nil {
		lines = []string{}
	}
	a := map[string]any{"unit": unit + ".service", "lines": lines}
	if ps := m.mainProcs(); len(ps) > 0 && !strings.HasPrefix(ps[0].StartedIn, restartAs) && unit == restartAs {
		a["note"] = fmt.Sprintf("the running Betterbird (pid %d) was not started by the module: it runs in %s, "+
			"and its output goes where status says (output), not to this journal; betterbird_restart starts it as %s",
			ps[0].PID, ps[0].StartedIn, restartAs)
	}
	return a, nil
}

// RestartAnswer is what betterbird_restart answers.
type RestartAnswer struct {
	// Composers are the message windows that were open: what was unsent and is gone.
	Composers int     `json:"composers_discarded,omitempty"`
	Note      string  `json:"note,omitempty"`
	Ended     []int   `json:"ended"`
	Killed    []int   `json:"killed,omitempty"`
	UserJS    string  `json:"user_js"`
	Running   []Proc  `json:"running"`
	Session   Session `json:"session"`
	Unit      string  `json:"unit"`
}

// composerClass is the X instance of a message being written.
var composerClass = regexp.MustCompile(`\("Msgcompose" "eu\.betterbird\.Betterbird"\)`)

// composers counts the open message windows, from the X window tree.
func (m *Machine) composers(s Session) (int, error) {
	o := m.cmd(5*time.Second, s.Env(), "xwininfo", "-root", "-tree")
	if err := failed(o, "xwininfo", "-root", "-tree"); err != nil {
		return 0, err
	}
	return len(composerClass.FindAllString(o.Stdout, -1)), nil
}

// Restart ends Betterbird (asked to quit, forced after 10 s), places the module's user.js when it can,
// and starts Betterbird again in the operator's session under the account's service manager, its output
// in the journal. While a message is being written it refuses, unless discard says the unsent may go.
// It answers within the runtime's 30 s: a start that has not shown after 4 s is said, and
// betterbird_status sees it come.
func (m *Machine) Restart(discard bool) (RestartAnswer, error) {
	s, err := m.session()
	if err != nil {
		return RestartAnswer{}, err
	}
	a := RestartAnswer{Session: s, Unit: restartAs + ".service"}
	n, err := m.composers(s)
	switch {
	case err != nil && !discard:
		return a, fmt.Errorf("whether a message is being written cannot be told (%v): restart with discard_unsent only if none is", err)
	case n > 0 && !discard:
		return a, fmt.Errorf("%d composer window(s) are open: an unsent message would be lost. Send or save it, or ask the operator, then call again with discard_unsent", n)
	}
	a.Composers = n
	a.Ended, a.Killed = m.stopProcs(10*time.Second, m.mainProcs())
	if u, err := m.userJS(true); err != nil {
		a.UserJS = "not placed: " + err.Error()
	} else {
		a.UserJS = fmt.Sprintf("placed: %d preference(s) from ~/%s", u.Statements, declared)
	}
	if err := m.detach(s, restartAs, startBin); err != nil {
		return a, err
	}
	for waited := time.Duration(0); waited < 4*time.Second && len(m.mainProcs()) == 0; waited += 250 * time.Millisecond {
		m.Sleep(250 * time.Millisecond)
	}
	a.Running = m.mainProcs()
	if a.Running == nil {
		a.Running = []Proc{}
	}
	if len(a.Running) == 0 {
		a.Note = "started as " + a.Unit + "; no main process yet after 4 s: betterbird_status shows it once it runs, betterbird_log says why if it does not"
	}
	return a, nil
}

// CheckAnswer is what betterbird_check answers.
type CheckAnswer struct {
	OK       bool      `json:"ok"`
	Findings []Finding `json:"findings"`
}

// Check verifies what the module promises: Betterbird installed, one running in the session, its
// profile found, the module's user.js declared, valid, placed and in effect, and its output read.
func (m *Machine) Check() (CheckAnswer, error) {
	a := CheckAnswer{Findings: []Finding{}}
	add := func(what, do string) { a.Findings = append(a.Findings, Finding{what, do}) }
	v, err := m.installed(packageFor)
	if err != nil {
		return a, err
	}
	if v == "" {
		add("Betterbird ("+packageFor+") is not installed", "install it from the AUR: the node-engine installs packages from the official repositories only, so the module does not")
	}
	ps := m.mainProcs()
	switch {
	case len(ps) == 0:
		add("Betterbird is not running", "start it from the launcher, or betterbird_restart")
	case len(ps) > 1:
		add(fmt.Sprintf("%d Betterbird main processes run", len(ps)), "one profile is held by one process: betterbird_restart")
	}
	u, err := m.userJS(false)
	switch {
	case err != nil:
		add("no profile: "+err.Error(), "start Betterbird once")
	case !u.Present:
		add("the module's user.js is not on this machine (~/"+declared+")", "the module is not pushed here: the controller's push")
	case u.Valid != "":
		add("the module's user.js is refused: "+u.Valid, "change the module's setting prefs")
	case !strings.HasPrefix(u.Placed, "the module's, as declared"):
		add("the profile's user.js is "+u.Placed, "betterbird_user_js with apply, then betterbird_restart")
	case strings.HasPrefix(u.Effective, "not yet"):
		add("the module's user.js is placed but not in effect: "+u.Effective, "betterbird_restart")
	}
	if len(ps) > 0 {
		for _, s := range m.streams(ps[0].PID) {
			if s.Dead {
				add(fmt.Sprintf("Betterbird's fd %d is a pipe nobody reads (a session started before its output went to the journal): what it prints is lost", s.FD),
					"betterbird_restart, which starts it with its output in the journal")
			}
		}
	}
	a.OK = len(a.Findings) == 0
	return a, nil
}